Among the arthropod-borne flaviviruses, the four dengue virus serotypes, dengue type 1 virus (DENV-1), dengue type 2 virus (DENV-2), dengue type 3 virus (DENV-3), and dengue type 4 virus (DENV-4), which constitute a serologically distinct subgroup are most important in terms of human morbidity and geographic distribution. Dengue viruses cause dengue outbreaks and major epidemics in most tropical and subtropical areas where Aedes albopictus and Aedes aegypti mosquitos are abundant. Dengue infection produces fever, rash, and joint pain in humans. A more severe and life-threatening form of dengue, characterized by hemorrhagic fever and hemorrhagic shock, has occurred with increasing frequency in Southeast Asia and Central and South America, where all four dengue virus serotypes circulate. The underlying cause of severe dengue remains controversial (Halstead, S. 1982 Progress in Allergy. 31:301-364; Rosen, L 1986 Am. J. Trop. Med. Hyg. 35:642-653). An association of severe dengue with increased viral replication has been reported recently (Wang, W. K. et al. 2002 J. Virol. 76:4662-4665). A safe and effective vaccine against dengue is currently not available.
The dengue virus contains a positive strand RNA genome, coding for a polyprotein that is cleaved co- and post-translationally by a combination of cellular and viral proteases to generate the individual viral proteins (Markoff, L. 1989 J. Virol. 63:3345-3352; Chambers, T. J. et al. 1990. Ann. Rev. Microbiol. 44:649-688; Falgout, B. et al. 1991 J. Virol. 65:2467-2475). Dengue virus prM and E structural proteins and nonstructural NS1 protein are glycosylated. The prM glycoprotein is further cleaved by the cellular enzyme furin following viral assembly, generating M, which is present in the mature virus (Stadler, K. et al. 1997 J. Virol. 71:8475-8481). Flavivirus prM and E form heterodimers, which are assembled into viral particles during infection (Wengler, G. and G. Wengler 1989 J. Virol. 63:2521-2526). In this manner, the prM serves to protect the functional integrity of E from acid-induced conformational change (Heinz, F. X. et al. 1994 Virology 198:109-117; Holzmann, H. et al. 1995 Arch. Virol. 140:213-221). The E glycoprotein is responsible for cell attachment, possibly mediated by a receptor, and for fusion with the cell membranes following viral entry.
Mouse monoclonal antibodies against the dengue viruses have been valuable for dengue virus serotype determination (Gentry, M. K. et al. 1982 Am. J. Trop. Med. Hyg. 31:548-555; Henchal, E. A. et al. 1982 Am. J. Trop. Med. Hyg. 31:830-836). Studies in which monoclonal antibodies were used against dengue virus and other flaviviruses have also provided valuable information concerning the antigenic structure of the major viral antigen E (Heinz, F. X. et al 1983 Virology 126:525-537; Henchal, E. A. et al. 1985 Am. J. Trop. Med. Hyg. 34:162-169; Heinz, F. X. 1986 Adv. Virus Res. 31:103-168; Mandl, C. W. et al. 1989 J. Virol. 63:564-571; Roehrig, J. T. et al. 1998 Virology 246:317-328). The three-dimensional structure of the E glycoprotein has been determined at 2 Å resolution for tick-borne encephalitis virus and recently for dengue type 2 virus (Rey, P. A. et al. 1995 Nature 375:291-298; Modis, Y. et al. 2003 Proc. Natl. Acad. Sci. USA 100:6986-6991). These studies showed that the monomeric E polypeptide is folded into three distinct domains and that the E glycoprotein consists of a flat, elongated dimer structure with an interdomain ligand-binding pocket.
Monoclonal antibodies reactive to flavivirus envelope proteins have been shown to mediate protection against homologous virus challenge in animal models (Mathews, J. H. and J. T. Roehrig 1984 J. Immunol. 132:1533-1537; Brandriss, M. W. et al. 1986 J. Gen. Virol. 67:229-234; Gould, E. A. et al. 1986 J. Gen. Virol. 67:591-595; Kaufman, B. M. et al. 1987 Am. J. Trop. Med. Hyg. 36:427-434; Kimura-Kuroda, J., and K. Yasui 1988 J. Virol. 141:3606-3610). In most cases, protection by passive immunization has been correlated with the ability of these antibodies to neutralize the virus in vitro. Protection against dengue virus challenge was also demonstrated in mice following passive immunization with monoclonal or polyclonal antibodies specific to prM (Bray, M., and C. J. Lai. 1991 Virology 185:505-508; Kaufman, B M et al. 1987 Am. J. Trop. Med. Hyg. 36:427-434) or NS1 (Falgout, B. et al. 1990. J. Virol. 64:4356-4363; Henchal, E. A. et al. 1988 J. Gen. Virol. 69:2101-2107).
Most research efforts directed to the development of an attenuated live dengue vaccine have not yielded a satisfactory result. Recently, clinical evaluation was conducted on a genetically engineered DENV-4 mutant containing a 30-nucleotide deletion in the 3′ non-coding region that exhibited reduced replicative capacity in simian cell culture and in primates (Durbin, A. P. et al. 2001 Am. J. Trop. Med. Hyg. 65:405-413; Men R., et al. 1996 J. Virol. 70:3930-3937). Following a single-dose inoculation, a total of 20 volunteers remained afebrile and exhibited very few clinical signs. Each of the vaccinees developed a high titer of DENV-4 neutralizing antibodies four to six weeks after immunization. However, five vaccinees showed an elevation of serum levels of the liver enzyme alanine transaminase (ALT). The ALT elevations were mostly transient and eventually subsided, but there remains a concern about the safety of a live dengue virus vaccine. Passive immunization with clinically acceptable dengue virus neutralizing antibodies provides an attractive alternative to prevention of dengue virus infection. Highly efficient neutralizing antibodies might also be useful for consideration as a possible therapy for severe dengue virus infection. Recently, a phage display of combinatorial antibody libraries has allowed for the isolation of antibodies against important viral pathogens from human or non-human primates (Persson, M. A. et al. 1991 Proc. Natl. Acad. Sci. 88:2432-2436; Williamson, R. A. et al. 1993 Proc. Nat. Acad. Sci. 90:41413-4145 [Erratum 91:1193, 1994]; Burton, D. R. et al. 1994 Science 266:1024-1027; Crowe, J. E. Jr. et al. 1994. Proc. Natl. Acad. Sci. 91:1386-1390; Maruyama, T. et al. 1999 J. Virol. 73:6024-6030; Schofield, D. J. et al. 2000 J. Virol. 74:5548-5555).